Method and apparatus for performing efficient layer 2 function in mobile communication system

ABSTRACT

The present disclosure relates to a communication technique for converging IoT technology with a 5G communication system for supporting a higher data transfer rate beyond a 4G system, and a system therefor. The present disclosure can be applied to intelligent services (e.g., smart homes, smart buildings, smart cities, smart or connected cars, health care, digital education, retail business, and services associated with security and safety) on the basis of 5G communication technology and IoT-related technology. Disclosed are a method and an apparatus for configuring an efficient hierarchical layer  2  architecture and main functions thereof in a next-generation mobile communication system.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 17/073,751, filed on Oct. 19, 2020, which has issued as U.S. Pat.No. 11,291,075 on Mar. 29, 2022; which is a continuation application ofprior application Ser. No. 16/302,483, filed on Nov. 16, 2018, which hasissued as U.S. Pat. No. 10,820,370 on Oct. 27, 2020; and which is a 371of an International application number PCT/KR2017/005190, filed on May18, 2017 and is based on and claims priority under 35 U.S.C § 119(a) ofa Korean patent application number 10-2016-0061054, filed on May 18,2016, in the Korean Intellectual Property Office, the disclosure ofwhich is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a method and apparatus for facilitatingefficient operations of a terminal and a base station in a mobilecommunication system.

BACKGROUND ART

To meet the increased demand for wireless data traffic since thedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a “Beyond 4G Network” or a“Post LTE System”. Implementation of the 5G communication system inhigher frequency (mmWave) bands, e.g., 60 GHz bands, is being consideredin order to accomplish higher data rates. To decrease propagation lossof the radio waves and increase the transmission distance, beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMO(FD-MIMO), array antenna, analog beam forming, and large scale antennatechniques are being discussed for the 5G communication system. Inaddition, in the 5G communication system, there are developments underway for system network improvement based on advanced small cells, cloudRadio Access Networks (RANs), ultra-dense networks, device-to-device(D2D) communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP), reception-endinterference cancellation, and the like. In the 5G system, Hybrid FSKand QAM Modulation (FQAM) and sliding window superposition coding (SWSC)as advanced coding modulation (ACM) and filter bank multi carrier(FBMC), non-orthogonal multiple access (NOMA), and sparse code multipleaccess (SCMA) as advanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving into theInternet of Things (IoT) where distributed entities, such as things,exchange and process information without human intervention. TheInternet of Everything (IoE), which is a combination of IoT technologyand Big Data processing technology through connection with a cloudserver, has emerged. As technology elements, such as “sensingtechnology”, “wired/wireless communication and network infrastructure”,“service interface technology”, and “security technology” have beendemanded for IoT implementation, recently there has been research into asensor network, Machine-to-Machine (M2M) communication, Machine TypeCommunication (MTC), and so forth. Such an IoT environment may provideintelligent Internet technology services that create new values forhuman life by collecting and analyzing data generated among connectedthings. The IoT may be applied to a variety of fields including smarthome, smart building, smart city, smart car or connected cars, smartgrid, health care, smart appliances, and advanced medical servicesthrough convergence and combination between existing InformationTechnology (IT) and various industrial applications.

In line with these developments, various attempts have been made toapply the 5G communication system to IoT networks. For example,technologies such as a sensor network, Machine Type Communication (MTC),and Machine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be an example of convergencebetween the 5G technology and the IoT technology.

Recently, studies are being conducted on Layer 2 structure and its mainfunctions in line with the development of next generation mobilecommunication systems, and there is a need of an efficient Layer 2structure and a method and apparatus for facilitating the main functionsof Layer 2.

DISCLOSURE OF INVENTION Technical Problem

The present invention aims to provide a method for configuring anefficient Layer 2 structure and its main functions.

Solution to Problem

In accordance with an aspect of the present invention, a method fortransmitting a signal in a wireless communication system includeschecking segment offset (SO) information, generating a first layerprotocol data unit (PDU) including the SO information, and transmittingthe first layer PDU, wherein the first layer PDU includes at least oneheader and a second layer PDU group corresponding to the header and thesecond layer PDU group includes at least one second layer PDU.

In accordance with another aspect of the present invention, a method forreceiving a signal included in the wireless communication systemincludes receiving a first layer protocol data unit (PDU) includingsegment offset (SO) information, checking the SO information, andrecovering a second layer PDU from the first layer PDU based on the SOinformation, wherein the first layer PDU includes at least one headerand a second layer PDU group corresponding to the header and the secondlayer PDU group includes at least one second layer PDU.

In accordance with another aspect of the present invention, atransmitter for transmitting a signal in a wireless communication systemincludes a transmit unit configured to transmit the signal to a receiverand a controller configured to control to check segment offset (SO)information and generate a first layer protocol data unit (PDU)including the SO information and control the transmit unit to transmitthe first layer PDU, wherein the first layer PDU includes at least oneheader and a second layer PDU group corresponding to the header and thesecond layer PDU group includes at least one second layer PDU.

In accordance with still another aspect of the present invention, areceiver for receiving a signal in a wireless communication systemincludes a receive unit configured to receive a signal from atransmitter and a controller configured to control the receive unit toreceive a first layer protocol data unit (PDU) including segment offset(SO) information, check the SO information, and recover a second layerPDU from the first layer PDU based on the SO information, wherein thefirst layer PDU includes at least one header and a second layer PDUgroup corresponding to the header and the second layer PDU groupincludes at least one second layer PDU.

Advantageous Effects of Invention

The present invention is advantageous in terms of configuring anefficient Layer 2 structure and its main functions in a next generationmobile communication system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating architecture of a legacy LTE system;

FIG. 2 is a diagram illustrating a protocol stack in use for legacy LTEsystems;

FIG. 3 is a diagram illustrating a packet processing procedure in theradio protocol stack architecture of the legacy LTE system;

FIG. 4 is a diagram illustrating a packet segmentation or concatenationprocedure in the LTE layer of the legacy LTE system;

FIG. 5 is a diagram illustrating a proposed L2 protocol structureaccording to one embodiment of the present invention;

FIG. 6 is an operation flow diagram illustrating proposed L2 protocoloperation flows according to an embodiment of the present invention;

FIGS. 7A, 7B, and 7C are diagrams illustrating PDCP PDU formats in usefor the legacy LTE system;

FIG. 8 is a diagram illustrating a PDCP PDU format according to oneembodiment of the present invention;

FIGS. 9A and 9B are diagrams illustrating PDCP status report formats inuse for the legacy LTE system;

FIG. 10 is a diagram illustrating a proposed PDCP status report formataccording to one embodiment of the present invention;

FIG. 11 is a diagram illustrating multiplexed and segmented conceptualMAC PDUs according to one embodiment of the present invention;

FIG. 12 is a diagram illustrating a MAC PDU configured throughmultiplexing and segmentation in consideration of a header partaccording to one embodiment of the present invention;

FIG. 13 is a diagram illustrating a method for use of the 5G PDCP layerin common;

FIG. 14 is a diagram illustrating a method for use of the LTE (4G) PDCPlayer in common;

FIG. 15 is a block diagram illustrating a configuration of a UEaccording to an embodiment of the present invention; and

FIG. 16 is a block diagram illustrating a configuration of a basestation according to an embodiment of the present invention.

MODE FOR THE INVENTION

Exemplary embodiments of the present invention are described in detailwith reference to the accompanying drawings. The same reference numbersare used throughout the drawings to refer to the same or like parts.Detailed descriptions of well-known functions and structuresincorporated herein may be omitted to avoid obscuring the subject matterof the present invention.

Detailed descriptions of technical specifications well-known in the artand unrelated directly to the present invention may be omitted to avoidobscuring the subject matter of the present invention. This aims to omitunnecessary description so as to make clear the subject matter of thepresent invention.

For the same reason, some elements are exaggerated, omitted, orsimplified in the drawings and, in practice, the elements may have sizesand/or shapes different from those shown in the drawings. Throughout thedrawings, the same or equivalent parts are indicated by the samereference numbers.

Advantages and features of the present invention and methods ofaccomplishing the same may be understood more readily by reference tothe following detailed description of exemplary embodiments and theaccompanying drawings. The present invention may, however, be embodiedin many different forms and should not be construed as being limited tothe exemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this invention will be thorough andcomplete and will fully convey the concept of the invention to thoseskilled in the art, and the present invention will only be defined bythe appended claims. Like reference numerals refer to like elementsthroughout the specification.

It will be understood that each block of the flowcharts and/or blockdiagrams, and combinations of blocks in the flowcharts and/or blockdiagrams, can be implemented by computer program instructions. Thesecomputer program instructions may be provided to a processor of ageneral-purpose computer, special purpose computer, or otherprogrammable data processing apparatus, such that the instructions thatare executed via the processor of the computer or other programmabledata processing apparatus create means for implementing thefunctions/acts specified in the flowcharts and/or block diagrams. Thesecomputer program instructions may also be stored in a non-transitorycomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the non-transitorycomputer-readable memory produce articles of manufacture embeddinginstruction means that implement the function/act specified in theflowcharts and/or block diagrams. The computer program instructions mayalso be loaded onto a computer or other programmable data processingapparatus to cause a series of operational steps to be performed on thecomputer or other programmable apparatus to produce a computerimplemented process such that the instructions that are executed on thecomputer or other programmable apparatus provide steps for implementingthe functions/acts specified in the flowcharts and/or block diagrams.

Furthermore, the respective block diagrams may illustrate parts ofmodules, segments, or codes including at least one or more executableinstructions for performing specific logic function(s). Moreover, itshould be noted that the functions of the blocks may be performed in adifferent order in several modifications. For example, two successiveblocks may be performed substantially at the same time, or may beperformed in reverse order according to their functions.

According to various embodiments of the present invention, the term“module”, means, but is not limited to, a software or hardwarecomponent, such as a Field Programmable Gate Array (FPGA) or ApplicationSpecific Integrated Circuit (ASIC), which performs certain tasks. Amodule may advantageously be configured to reside on the addressablestorage medium and configured to be executed on one or more processors.Thus, a module may include, by way of example, components, such assoftware components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables. The functionalities of the components and modules may becombined into fewer components and modules or further separated intomore components and modules. In addition, the components and modules maybe implemented such that they execute one or more CPUs in a device or asecure multimedia card.

FIG. 1 is a diagram illustrating architecture of a legacy LTE system.

In reference to FIG. 1, a radio access network of the LTE systemincludes evolved Node Bs (hereinafter, interchangeably referred to aseNB, node B, and base station) 100, 110, 120, and 130; a mobilitymanagement entity (MME) 140; and a serving gateway (S-GW) 150. A userterminal (hereinafter, interchangeably referred to as user equipment(UE) and terminal) 160 connects to an external network via the eNBs 100,110, 120, and 130 and the S-GW 150.

The eNBs 100, 110, 120, and 130 correspond to the legacy node Bs of theuniversal mobile telecommunications system (UMTS). The UE 160 connectsto one of the eNBs via a radio channel, and the eNB has more complexfunctions than the legacy node B. In the LTE system where all usertraffic including real time services such as Voice over IP (VoIP) isserved through shared channels, there is a need of an entity forcollecting UE-specific status information (such as buffer status, powerheadroom status, and channel status) and scheduling the UEs based on thecollected information, and the eNB takes charge of such functions.Typically, one eNB hosts multiple cells. For example, the LTE systemadopts Orthogonal Frequency Division Multiplexing (OFDM) as a radioaccess technology to secure a data rate of up to 100 Mbps in a bandwidthof 20 MHz. The LTE system also adopts Adaptive Modulation and Coding(AMC) to determine the modulation scheme and channel coding rate inadaptation to the channel condition of the UE. The S-GW 150 handles databearer functions to establish and release a data bearer under thecontrol of the MME 140. The MME 140 handles various control functionsfor the UE as well as the mobile management function and has connectionswith the eNBs.

FIG. 2 is a diagram illustrating a protocol stack in use for legacy LTEsystems.

As shown in FIG. 2, the protocol stack of the interface between the UEand the eNB in the LTE system comprises a packet data convergencecontrol (PDCP) layer denoted by reference numbers 200 and 250, a radiolink control (RLC) layer denoted by reference numbers 210 and 260, and amedium access control (MAC) layer denoted by reference numbers 230 and270. The PDCP layer denoted by reference numbers 200 and 250 takescharge of compressing/decompression an IP header. The main functions ofthe PDCP layer are summarized as follows:

-   -   Header compression and decompression: ROHC only;    -   Transfer of user data;    -   In-sequence delivery of upper layer PDUs at PDCP        re-establishment procedure for RLC AM;    -   For split bearers in DC (only support for RLC AM): PDCP PDU        routing for transmission and PDCP PDU reordering for reception;    -   Duplicate detection of lower layer SDUs at PDCP re-establishment        procedure for RLC AM;    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at PDCP data-recovery procedure, for RLC AM;    -   Ciphering and deciphering;    -   Timer-based SDU discard in uplink.

The RLC layer denoted by reference numbers 210 and 260 takes charge ofreformatting PDCP PDUs in order to fit them into the size for ARQoperation. The main functions of the RLC layer are summarized asfollows:

-   -   Transfer of upper layer PDUs;    -   Error Correction through ARQ (only for AM data transfer);    -   Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer);    -   Re-segmentation of RLC data PDUs (only for AM data transfer);    -   Reordering of RLC data PDUs (only for UM and AM data transfer);    -   Duplicate detection (only for UM and AM data transfer);    -   Protocol error detection (only for AM data transfer);    -   RLC SDU discard (only for UM and AM data transfer);    -   RLC re-establishment.

The MAC layer denoted by reference numbers 230 and 270 allows forconnection of multiple RLC entities established for one UE and takescharge of multiplexing RLC PDUs from the RLC layer into a MAC PDU anddemultiplexing a MAC PDU into RLC PDUs. The main functions of the MAClayer are summarized as follows:

-   -   Mapping between logical channels and transport channels;    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels;    -   Scheduling information reporting;    -   Error correction through HARQ;    -   Priority handling between logical channels of one UE;    -   Priority handling between UEs by means of dynamic scheduling;    -   MBMS service identification;    -   Transport format selection;    -   Padding.

The physical (PHY) layer denoted by reference numbers 240 and 280 takescharge of channel-coding and modulation on higher layer data to generateand transmit OFDM symbols over a radio channel, and demodulating andchannel-decoding on OFDM symbols received over the radio channel todeliver the decoded data to the higher layers.

FIG. 3 is a diagram illustrating a packet processing procedure in theradio protocol stack architecture of the legacy LTE system.

A packet sent down to the PDCP layer 300 is referred to as PDCP servicedata unit (SDU). The PDCP SDU may contain an IP packet (user plane) orRRC control information (control plane). The user plane data may undergoheader compression. The header compression operation is taken to reducethe packet size by compressing the header. It may also be possible toundergo ciphering and an integrity protection operation. The cipheringoperation is taken for ciphering the packet in order for a specificreceiver to receive the packet correctly. The ciphering operation isperformed to the payload of the PDCP PDU and MAC-I but not to the PDCPControl PDU. The integrity protection operation is taken for determiningwhether the packet is corrupted with wrong information. The integrityprotection operation is performed to the header and payload of the PDCPPDU before the ciphering. A PDCP header is added to obtain a PDCP PDU.

The RLC layer 310 processes (segments or concatenates) the PDCP PDU(=RLC SDU) received from the PDCP layer into the size indicated by theMAC layer 320 to generate an RLC PDU. The segmentation and concatenationoperations being performed in the RLC layer are described in detail withreference to FIG. 4. An RLC header is added to obtain the RLC PDU. TheMAC layer 320 generates a MAC PDU composed of a MAC header and MACpayload. The MAC header contains MAC sub-headers corresponding to MACcontrol elements (CEs) and or MAC SDUs.

FIG. 4 is a diagram illustrating a packet segmentation or concatenationprocedure in the LTE layer of the legacy LTE system.

The RLC layer receives RLC SDUs (or PDCP PDUs) 400 and 405 from the PDCPlayer. The RLC SDU is processed into the size as indicated by the MAClayer. In order to accomplish this, the RLC SDU may be segmented orconcatenated with other RLC SDUs or a segment of another RLC SDU. Inthis embodiment, an AMD PDU being handled in association with ARQ isconsidered. For initial transmission, RLC SDU #1 and a segment of RLCSDU #2 are concatenated into one RLC PDU. The RLC PDU consists of an RLCheader 410 and an RLC payload 415. The RLC header includes properties ofthe RLC PDU and segmentation or concatenation information. That is, theRLC header includes a data/control (D/C) field, a re-segmentation flag(RF) field, a framing information (FI) field, a sequence number (SN)field, and a length indicator (LI) field.

The D/C field has a length of 1 bit for indicating whether the RLC PDUis a control PDU or a data PDU.

TABLE 1 Value Description 0 Control PDU 1 Data PDU

The RF field has a length of 1 bit for indicating whether the RLC PDU isan AMD PDU or an AMD PDT T segment

TABLE 2 Value Description 0 AMD PDU 1 AMD PDU segment

The FI field has a length of 2 bits for indicating whether the start andend of the RLC PDU are the start and end of the RLC PDU or an RLCsegment.

TABLE 3 Value Description 00 First byte of the Data field corresponds tothe first byte of a RLC SDU. Last byte of the Data field corresponds tothe last byte of a RLC SDU. 01 First byte of the Data field correspondsto the first byte of a RLC SDU. Last byte of the Data field does notcorrespond to the last byte of a RLC SDU. 10 First byte of the Datafield does not correspond to the first byte of a RLC SDU. Last byte ofthe Data field corresponds to the last byte of a RLC SDU. 11 First byteof the Data field does not correspond to the first byte of a RLC SDU.Last byte of the Data field does not correspond to the last byte of aRLC SDU.

The SN field indicates a sequence number of the RLC PDU.

The LI field is used for indicating the length of a segment of the RLCPDU, which has a length of 11 bits for RLC UM or 15 bits for RLC UM.Accordingly, the number of LI fields has to differ in proportion to thenumber of segments included in one RLC PDU.

The RLC payload includes the RLC SDU #1 and a segment of the RLC SDU #2,and the boundary between the two RLC SDUs is indicated by X1 420.

The RLC PDU generated as above is sent to the MAC layer. It may occurthat the RLC PDU is not delivered successfully so as to be retransmittedby ARQ. The RLC PDU may be re-segmented for ARQ retransmission. Thesegment obtained through re-segmentation may be referred to as an AMDPDU segment for distinction from the normal AMD PDU. For example, theAMD PDU to be retransmitted as a result of transmission failure may besegmented into two AMD PDU segments for retransmission. In this case,the first AMD PDU segment carries the RLC payload part 430 with the sizeof Y1 of the default AMD PDU, and the second AMD PDU segment carries theremaining RLC payload part with the exception of the size of Y1. Thesecond AMD PDU segment may include part (X1−Y1) of the original RLC SDU#1 400 as denoted by reference numbers 420 and 430 and part of the RLCSDU #2 405.

The AMD PDU segments also have RLC headers 425 and 435, each includingthe D/C field, the RF field, the FI field, the SN field, a last segmentflag (LSF) field, a segment offset (SO) field, and the LI field. Unlikethe RLC header of the AMD PDU, the RLC header of the AMD PDU segmentfurther includes the LSF field and SO field.

The SSF field has a length of 1 bit for indicating whether the last byteof the AMD PDU segment is identical with the last byte of the AMD PDU.

TABLE 4 Value Description 0 Last byte of the AMD PDU segment does notcorrespond to the last byte of an AMD PDU. 1 Last byte of the AMD PDUsegment corresponds to the last byte of an AMD PDU.

The SO field has a length of 15 or 16 bits for indicating the originalposition of the AMD PDU segment in the AMD PDU. In FIG. 4, the SO fieldis set to 0 (byte) in the first AMD PDU segment header and Y1 in thesecond AMD PDU segment header. The AMD PDU header, the first AMD PDUsegment, and the second AMD PDU header have the information fields setto the values as denoted, respectively, by reference numbers 445, 450,and 455.

The main functions of the above-described PDCP and RLC layers of thelegacy LTE may be summarized as follows: security, ARQ, re-ordering, andduplicate detection in the PDCP layer; and ARQ, re-ordering, duplicatedetection, and segmentation and concatenation in the RLC layer. The PDCPlayer may perform retransmission in a predetermined situation such asPDCP reestablishment.

In order to meet the requirement for efficient packet transmission inthe next generation mobile communication system, it is necessary tosimplify the protocol stack and eliminate redundant functions appearingon multiple protocol layers in the legacy LTE protocol stack. Actually,the segmentation and concatenation operations of the RLC layer causesignificant overhead in the legacy LTE protocol stack and thus there isa necessity to consider concentrating the operations performedredundantly in the PDCP and RLC layers into one of them.

The present invention proposes a novel L2 protocol structure composed ofa PDCP layer with improved functionalities and a MAC layer instead ofthe legacy RLC layer for use in the next generation mobile communicationsystem. In the new L2 protocol structure, the PDCP layer takes charge ofARQ, reordering, and duplicate detection operation in addition to itsoriginal functions. Because it communicates with the MAC layer directly,the PDCP layer also has to be responsible for the HARQ reorderingoperation; whereas the MAC layer is responsible for the segmentation andconcatenation operations that have been taken by the LTE RLC layer withthe exclusion of the RLC SDU re-segmentation operation entailed by theretransmission mechanism. This is because the ARQ operation is performedwith PDCP PDUs as opposed to RLC PDUs. In order to communicate directlywith the PDCP layer, the new MAC layer has to take charge ofmultiplexing and demultiplexing PDCP PDUs.

FIG. 5 is a diagram illustrating a proposed L2 protocol structureaccording to one embodiment of the present invention. As shown in FIG.5, a control packet (control plane) is generated by the RRC layer 500 oran upper layer 540, and a common control packet belonging to a commoncontrol channel (CCCH) 530 is directly sent down to the MAC layer 520logically without passing through the PDCCH layer 510. In contrast, adedicated control packet belonging to a dedicated control channel (DCCH)550 is sent down to the MAC layer via the PDCP layer 510. Meanwhile, adata packet 560 (user plane) belonging to a dedicated traffic channel(DCCH) 570 is sent down to the MAC layer via the PDCP layer.

FIG. 6 is an operation flow diagram illustrating proposed L2 protocoloperation flows according to an embodiment of the present invention. Inreference to FIG. 6, if a packet 600 arrives at the transmit end, thePDCP layer performs header compression at step 605, ciphering at step610, and PDCP header addition at step 615. The PDCP PDU generated inthis way is stored in a transmit buffer at step 620. The PDCP layersends down the PDCP PDUs stored in the buffer to the MAC layer as alower layer according to a first-in first-out (FIFO) rule. The PDCP PDUssent downlink to the MAC layer are kept, as opposed to being immediatelydiscarded, in the buffer for ARQ retransmission until a predeterminedcondition is fulfilled.

If the PDCP PDUs are received, the MAC layer performs segmentation orconcatenation at step 625 according to the MAC PDU size. Afterward, theMAC layer adds a MAC header to generate a MAC PDU at step 630. The MACheader may include certain fields that are not included in the legacyMAC header because the MAC layer is responsible for segmentation andconcatenation operations. The newly added fields are described later.

At the receive end, the MAC layer removes the MAC headers from thereceived MAC PDUs and performs demultiplexing at step 635. The PDCP PDUconveyed in multiple MAC PDUs is reassembled (if necessary) at step 640.The reassembled PDCP PDU is delivered to the PDCP layer. The PDCP layerstores the PDCP PDU in a receive buffer at step 645. The PDCP PDU is notdelivered to the PDCP layer in order of SN because the HARQ operation isperformed in the MAC layer. Accordingly, there is a need of a reorderingoperation. The PDCP layer performs duplicate detection and redundantPDCP PDU removal for the case where redundant PDCP PDUs are deliveredfrom the MAC layer. At the receive end, if no PDCP PDU is received untila predetermined condition is fulfilled or a predetermined time expires,the PDCP layer may transmit feedback information to the transmit end forARQ retransmission. The feedback information includes the information onthe missing PDCP PDUs in the form of a bitmap. Upon receipt of thefeedback information, the transmit end retransmits the missing PDCPPDUs. Since the whole PDCP PDU is retransmitted, the necessity of there-segmentation that has been performed in the legacy RLC layer isobviated. The PDCP layer performs PDCP header removal at step 650,deciphering at step 655, and decompression at step 660 on thesuccessfully received PDCP PDU to recover the PDCP SDU at step 665.

FIGS. 7A, 7B, and 7C are diagrams illustrating PDCP PDU formats in usefor the legacy LTE system.

The PDCP data PDU format has a PDCP SN 710 that differs in length. ThePDCP SN is set when the RB is established. As an option, MAC-I may beincluded in the PDCP data PDU. FIG. 7A shows a user plane PDCP data PDUformation with a 7-bit PDCP SN. FIG. 7B shows a user plane PDCP data PDUformation with a 12-bit PDCP SN. In FIG. 7B, the first octet includes 3reserved bits 730. FIG. 7 shows a user plane PDCP data PDU with a 15-bitPDCP SN. The PDCP SN is followed by data 710, and every PDCP PDUincludes a D/C field 700.

FIG. 8 is a diagram illustrating a PDCP PDU format according to oneembodiment of the present invention.

It may be assumed that the next generation mobile communication systemsupports a high speed transmission that is faster than ever before. Thismeans that the system is likely to run short of legacy PDCP SNs having alength up to 15 bits. Accordingly, there is a need of a PDCP data PDUformation with a PDCP SN longer than 15 bits. The present inventionproposes a PDCP data PDU format 800 including a D/C field and 5 reservedbits in the first octet, the reserved bits being followed by an 18-bitPDCP SN.

FIGS. 9A and 9B are diagrams illustrating PDCP status report formats inuse for the legacy LTE system.

In the legacy LTE system, PDCP status report and RLC status PDUs aredefined for supporting a retransmission scheme. Such PDU formats aim tonotify the transmitter of missing packets. The legacy RLC STATUS PDU ischaracterized by including SNs of the missing packets (RLC PDUs) andSOstart and SOend fields for indicating the missing portion per SN.

For the next generation mobile communication system assuming ahigh-speed transmission, considering that a missing MAC PDU, althoughrarely occurring, causes a large number of missing PDCP PDUsconcatenated therein, there is likely to be a preference for defining anew format based on the legacy PDCP status report format rather thanusing the legacy RLC STATUS PDU format designed for carrying SNs of allmissing packets.

FIG. 9A shows a PDCP status report format with a 18-bit SN. The PDCPstatus report is transmitted when a PDCP re-establishment is requested,a polling bit (P) field set to 1 is received, or a t-StatusReportType1timer expires. This PDCP status report format includes a D/C field 900,a PDU type field 910, a first missing PDCP SN (FMS) field 930, and abitmap field 940.

The PDU type field has a length of 3 bits for indicating a type of thePDU. The type of PDU is indicated as in Table 5.

TABLE 5 Bit Description 000 PDCP status report 001 Interspersed ROHCfeedback packet 010 LWA status report 011-111 reserved

The FMS field is identical in bitwidth with the SN field and used toindicate the PDCP SN of the first missing PDCP SDU.

The bitmap field has a zero-length variable length. This field is usedto indicate the successfully received PDCP SDUs following the PDCP SDUindicated via the FMS field. For example, the MSB of the first octet ofthis field is used to indicate whether the PDCP SDU with the PDCP SN of(FMS+1) modulo (Maximum_PDCP_SN+1) is received. The LSP of the firstoctet of this field is used to indicate whether the PDCP SDU with thePDCP SN of (FMS+8) modulo (Maximum_PDCP_SN+1) is received. Each bit ofthe bitmap field is set for the purpose of indication as follows.

TABLE 6 Bit Description 0 PDCP SDU with PDCP SN = (FMS + bit position)modulo (Maximum_PDCP_SN + 1) is missing in the receiver. The bitposition of N^(th) bit in the Bitmap is N, i.e., the bit position of thefirst bit in the Bitmap is 1. 1 PDCP SDU with PDCP SN = (FMS + bitposition) modulo (Maximum_PDCP_SN + 1) does not need to beretransmitted. The bit position of N^(th) bit in the Bitmap is N, i.e.,the bit position of the first bit in the Bitmap is 1.

FIG. 9B shows a PDCP status report formation with a 15-bit SN in use forLTE-Wi-Fi link aggregation (LWA) technology. This PDCP status report istransmitted when a polling bit (P) field set to 1 is received or at-StatusReportType2 timer expires. This PDCP status report formatincludes a highest received SN on WLAN (HRW) and a number of missing(PDUs) fields in addition to the information fields of the PDCP statusreport format of FIG. 9A.

The NMP field is identical in bitwidth with the SN field and used toindicate the number of missing PDCP PDUs from the PDCP PDU indicated bythe FMS

FIELD

The HRW field is identical in bitwidth with the SN field and used toindicate the PDCP SN of the PDCP SDU received via a WLAN with thehighest PDCP COUNT value.

However, the legacy PDCP status report is not appropriated for the ARQoperation in the next generation mobile communication system assuminghigh-speed transmission. This is the case particularly when consideringthat PDCP PDU loss occurs rarely, but if it does occur a large number ofPDCP PDUs are missing in a concatenated manner. For example, if the nthPDCP PDU and the (n+16000)th PDCP PDU are missing, this means that thebitmap field with a very large length of 2000 bytes is required.Furthermore, the status report for the LWA is designed for flow controlas opposed to ARQ. Accordingly, it may be necessary to define the newformat indicative of the missing PDCP PDUs and report triggerconditions, by referring to the legacy PDCP status report.

FIG. 10 is a diagram illustrating a proposed PDCP status report formataccording to one embodiment of the present invention.

Considering that PDCP PDU loss occurs rarely, but if it does occur alarge number of PDCP PDUs are lost in a concatenated manner asaforementioned, the present invention proposes a method of indicatingthe SN of the first missing PDCP PDU and the number of consecutivemissing PDCP PDUs. Also, it should be possible for a PDCP status reportformat to indicate all of the sets of consecutive missing PDCP PDUs.

The proposed format includes an ACK SN field 1015, missing SN (MS)fields 1025 and 1040 indicating the SNs of the first missing PDCP PDUsin the respective missing PDCP PDU sets, and NCMP (number of consecutivemissing PDUs) fields 1030 and 1045. An MS field is followed by an NCMPfield in a paired manner. That is, the NCMP field indicates the numberof missing PDUs starting from the first PDU indicated by the paired MSfield. The NCMP field may count the first missing PDCP PDU in or not.The PDCP status report format may include multiple MS and NCMP fields.

The proposed format includes a D/C field 1000, a PDU Type field 1005,and an ACK SN field 015. The D/C field is set to 0 for a control PDU,the PDU type field is set to 000 for the PDCP status report or one ofreserved values (011 to 111) for the new PDCP status report. The ACK SNfield is identical in definition with that included in the RLC STATUSPDU and indicates that the PDCP PDUs to the PDCP PDU indicated thereby,without exception of the missing PDCP PDU indicated by the MS and NCMPfields, are received at the receive end. In order to maintain the unityof the PDCP status report format, the reserved bits 1010, 1020, and 1030may be inserted. These reserved bits may be omitted, and the MS field,the NCMP field, and the ACK field may be defined differently in positionand length in the format as opposed to those shown in the drawing.

The proposed PDCP status report may be transmitted when a polling bit(P) field set to 1 is received or a t-StatusReportType3 timer expireswhen or after the last PDCP PDU stored in the PDCP transmit buffer istransmitted. The proposed PDCP status report may also be transmittedwhen the PDCP receive end detects a missing PDU. Also, a polling timermay be used for the polling operation. That is, the PDCP transmit endmay start a timer after transmitting a PDU including the polling bit (P)field set to 1 and, if the timer expires, it may transmit a PDUincluding the polling bit (P) field set to 1 again. After transmitting apredetermined number of PDUs or bytes, the transmit end may transmit aPDU including the polling bit (P) field set to 1. The PDCP receive endmay start a timer after transmitting the PDCP status report and, if thetimer expires, it may transmit the status report again.

Hereinafter, a description is made of the in-sequence delivery,duplicate detection, and HARQ reordering as PDCP functions.

The in-sequence delivery, duplicate detection, and reordering have beenalready defined (for dual connectivity in which the PDCP layer takescharge of reordering because one PDCP entity transmits/receives data viatwo RLC entities). If the split bearer is not configured, it may bepossible to set the reordering timer to a low value. For theoptimization purpose, it may be possible to start the t-ordering fromthe last missing PDU rather than the first missing PDU.

The above description has been made of the method for improving PDCPlayer operation in the proposed L2 protocol structure. The newlyproposed MAC layer has to perform demultiplexing, augmentation, andreassembly operations. The multiplexing operation requires a logicalchannel identifier (LCID) and a length field, and the segmentation andreassembly operations require the SN and segmentation information.

FIG. 11 is a diagram illustrating multiplexed and segmented conceptualMAC PDUs according to one embodiment of the present invention. In FIG.11, each MAC PDU contains a plurality of PDCP PDUs that are distinctivein color. The PDCP PDUs that have the same color belong to one MAC SDUgroup with the same priority. The multiple PDCU PDUs 1100 to 1105belonging to one MAC SDU group occupy part of the MAC PDU 1, and theother PDCP PDUs 1110 to 1115 belonging to another MAC SDU group occupythe remaining part of the MAC PDU 1. Such an arrangement may beperformed according to the priorities of the MAC SDUs.

If the last PDCP PDU cannot be wholly included in the MAC PDU 1, it maybe segmented such that a segment 1115 of the last PDCP PDU is includedin the MAC PDU 1. Similarly, another segment 1130 of the last PDCP PDUis included in the MAC PDU 2, and the last segment 1150 of the last PDCPPDU is included in the last MAC PDU 3. Considering the multiplexing andsegmentation operations, the header has to include the informationnecessary for demultiplexing and assembly at the receive end. Althoughthe drawing shows a conceptual MAC PDU, the MAC PDU has to have a headercontaining the necessary information at the beginning or a predeterminedpart thereof.

FIG. 12 is a diagram illustrating a MAC PDU configured throughmultiplexing and segmentation in consideration of a header partaccording to one embodiment of the present invention. According to thelegacy technology, sub-headers corresponding to the respective MAC CEsand/or MAC SDUs (logical channel) are all located at the beginning ofthe MAC PDU, and each sub-header has an E field for indicating whetheranother sub-header or MAC CE or MAC SDU follows.

In the present invention, the MAC SDU groups (logical channel) haverespective sub-headers 1200 and 1210 at the beginnings thereof in orderto avoid the overhead caused by the E field being inserted persub-header. Each sub-header may include an LCID field 1220, a field 1225indicating the number of PDCP PDUs in the MAC SDU 1225, a field 1230indicating the length of the PDCP PDU or segmented PDCP PDU, and an S1field 1235. The S1 field has a length of 1 bit and indicates whether theMAC SDU includes a segmented PDCP PDU. It may be possible to add atleast one of a last or first field 1240, a last segment flag (LSF) field1245, an SN field 1250, and a segment offset (SO) field 1255 dependingon whether or not the segmented PDCP PDU exists.

The last or first field 1240 is used to indicate whether the segmentedPDCP PDU is at the beginning or end of the MAC SDU group. The LSF field1245 indicates whether the last byte of the segmented PDCP PDU isidentical with the last part of the MAC SDU group as in Table 7.

TABLE 7 Value Description 0 Last byte of the PDCP PDU segment does notcorrespond to the last byte of an MAC SDU group. 1 Last byte of the PDCPPDU segment corresponds to the last byte of an MAC SDU group.

The SN field 1250 indicates the SN of the segmented PDCP PDU. The SOfield 1255 is used to indicate the location of the segmented PDCP PDU inthe original PDCP PDU.

The segmentation may be configured for uplink and downlink separatelybecause it is an operation incurring significant overhead in the L2layer. Considering 20 MHz DL system bandwidth, the maximum TB size is10992; assuming that the DL system bandwidth of the next generationmobile communication is 100 MHz, the maximum TB size becomes no lessthan 54960 bytes. Considering the IP packet size of 1500 bytes, the basestation may control the MAC PDU generation without the burdensomesegmentation operation in downlink. Accordingly, it may be possible toallow segmentation in downlink but not in uplink. Whether to configuresegmentation may be determined according to the TB size indicated by thebase station. If segmentation is configured, the S1 field should beincluded in the sub-header. Otherwise, it is not necessary to includethe SI field in the sub-header. The bit corresponding to the S1 fieldmay be used to indicate the length of the PDCP PDU.

That is, the MAC PDU format for the case of configuring segmentation andthe MAC PDU format for the case of not configuring segmentation maydiffer as follows. Various MAC PDU formats are possible and, accordingto an embodiment of the present invention, the MAC sub-header isincluded per PDCP PDU and includes the LCID field, the length field, andthe S1 field for the corresponding PDCP PDU.

-   -   If segmentation is configured, a predetermined field of the MAC        sub-header may be used to indicate the presence/absence of a        segmentation header. For example, the MAC sub-header may include        an n-bit LCID field, an m-bit length field, and 1-bit SI field        (first format).    -   If segmentation is not configured, a predetermined field (S1        field) of the MAC header may be used for a different purpose,        e.g., for expanding the field indicating the size of the MAC SDU        (or PDCP PDU) related to the MAC header. For example, the MAC        sub-header may include an n-bit LCID field and an (m+1)-bit        length field (second format).

Segmentation may be configured or not according to a predeterminedcondition or configured by the base station per UE. For example, it maybe possible to configure segmentation in uplink but not in downlink. Inthis case, the UE may generate uplink MAC PDUs with the first MACsub-header format and process downlink MAC PDUs assuming the second MACsub-header format. It may also be possible for the base station toconfigure whether to use segmentation or not in downlink per UE using anRRC control message under the assumption of the use of segmentation inuplink. It may also be possible that the information on whether to usesegmentation is delivered to unspecified UEs via system informationbeing broadcast by the base station.

It may also be possible to configure segmentation to be used if apredetermined condition is fulfilled. For example, it may be possible todetermine whether to use segmentation based on the size of the MAC PDU(or transport block). If the size of the MAC PDU to be transmitted bythe UE is shorter than x bytes, the UE generates the MAC PDU with thefirst MAC sub-header format; if the size of the MAC PDU is longer than xbytes, the UE generates the MAC PDU with the second MAC sub-headerformat without consideration of segmentation. If the size of the MAC PDUreceived by the UE is shorter than y bytes, the UE processes the MAC PDUunder the assumption of the first MAC sub-header format; if the size ofthe MAC PDU is longer than y bytes, the UE processes the MAC PDU underthe assumption of the second MAC sub-header format. The values of x andy are delivered from the base station to the UE via an RRC controlmessage or system information. The first and second MAC sub-headerformats differ in length of a predetermined information field (e.g.,length field and presence/absence of a predetermined field).

FIGS. 13 and 14 are diagrams for explaining interoperation with a legacyLTE system according to one embodiment of the present invention.

Similar to the RAN split in the legacy dual connectivity technology, theUE may transmit/receive data via LTE eNB and 5G base stationsimultaneously. In other to achieve this, the UE has to operate in theLTE system in a similar way to that in the 5G system.

FIG. 13 is a diagram illustrating a method for use in common of the 5GPDCP layer.

In reference to FIG. 13, the ARQ operation in the 5G PDCP layer 1300obviates the necessity of the ARQ operation in the 4G RLC layer 1310.Accordingly, the 4G RLC layer 1310 is configured to operate in the RLCunacknowledged mode (UM) in which the ARQ operation is not required.Also, the HARQ reordering operation in the 5G PDCP layer 1300 obviatesthe necessity of the HARQ reordering operation in the 4G RLC layer 1310.The proposed ARQ operation of the present invention is designed to yieldmaximum ARQ performance in the 5G PDCP layer 1300.

FIG. 14 is a diagram illustrating a method for use in common of the LTE(4G) PDCP layer.

In the case that the 4G PDCP layer is used in common, it is difficultfor the ARQ operation to be fully performed in the 4G PDCP layer 1400.For example, it is necessary to configure a periodic PDCP status reportand polling and even impossible to use the PDCP status report formatproposed in the present invention. Accordingly, although it is performedin the 4G PDCP layer, the ARQ operation is somewhat limited inperformance. The 4G RLC layer 1410 is configured to operate in the RLCUM mode requiring no ARQ, which obviates the necessity of the HARQreordering.

According to an embodiment of the present invention, a signaltransmission method of a transmitter in a wireless communication systemincludes checking segment offset (SO) information, generating a firstlayer protocol data unit (PDU) including the SO information, andtransmitting the first layer PDU, wherein the first layer PDU includesat least one of a header and a second layer PDU group corresponding tothe header, the second layer PDU group including at least one secondlayer PDU.

According to an embodiment of the present invention, a signal receptionmethod of a receiver in a wireless communication system includesreceiving a first layer protocol data unit (PDU) including segmentoffset (SO) information, ascertaining the SO information, and recoveringa second layer PDU from the first layer PDU based on the SO information,wherein the first layer PDU includes at least one header and a secondlayer PDU group corresponding to the header, the second layer PDU groupincluding at least one second layer PDU.

FIG. 15 is a block diagram illustrating a configuration of a UEaccording to an embodiment of the present invention.

In reference to FIG. 15, the UE includes a radio frequency (RF)processor 1500, a baseband processor 1510, a storage unit 1520, and acontroller 1530.

The RF processor 1500 has a function for transmitting/receiving a signalover a radio channel such as band conversion and amplification of thesignal. That is, the RF processing unit 1500 up-converts a basebandsignal from the baseband processor 1510 to an RF band signal andtransmits the RF signal via an antenna and down-converts the RF signalreceived via the antenna to a baseband signal. For example, the RFprocessor 1500 may include a transmission filter, a reception filter, anamplifier, a mixer, an oscillator, a digital-to-analog converter (DAC),and an analog-to-digital converter (ADC). Although one antenna isdepicted in FIG. 15, the UE may be provided with a plurality ofantennas. The RF processor 1500 may also include a plurality of RFchains. The RF processor 1500 may perform beamforming. For beamforming,the RF processor 1500 may adjust the phase and size of a signal to betransmitted/received by means of the antennas or antenna elements. TheRF processor 1500 may be configured to support a MIMO scheme with whichthe UE can receive multiple layers simultaneously.

The baseband processor 1510 has a baseband signal-bit string conversionfunction according to a physical layer standard of the system. Forexample, in a data transmission mode, the baseband processor 1510performs encoding and modulation on the transmission bit string togenerate complex symbols. In a data reception mode, the basebandprocessor 1510 performs demodulation and decoding on the baseband signalfrom the RF processor 1500 to recover the transmitted bit string. In thecase of using an OFDM scheme for data transmission, the basebandprocessor 1510 performs encoding and modulation on the transmission bitstring to generate complex symbols, maps the complex symbols tosubcarriers, performs inverse fast Fourier transform (IFFT) on thesymbols, and inserts a cyclic prefix (CP) into the symbols to generateOFDM symbols. In the data reception mode, the baseband processor 1510splits the baseband signal from the RF processor 1500 into OFDM symbols,performs fast Fourier transform (FFT) on the OFDM symbols to recover thesignals mapped to the subcarriers, and performs demodulation anddecoding on the signals to recover the transmitted bit string.

The baseband processor 1510 and the RF processor 1500 process thetransmission and reception signals as described above. Accordingly, thebaseband processor 1510 and the RF processor 1500 may be referred to asa transmitter, a receiver, a transceiver, or a communication unit. Atleast one of the baseband processor 1510 and the RF processor 1500 mayinclude a plurality of communication modules for supporting differentradio access technologies. At least one of the baseband processor 1510and the RF processor 1500 may also include multiple communicationmodules for processing the signals in different frequency bands. Forexample, the different radio access technologies may include a wirelesslocal area network (WLAN) (e.g., Institute of Electrical and ElectronicsEngineers (IEEE) 802.11) and a cellular network (e.g., LTE). Thedifferent frequency bands may include a super high frequency (SHF) band(e.g., 2.5 GHz and 5 GHz bands) and an mmWave band (e.g., 60 GHz).

The storage unit 1520 stores data such as basic programs for operationof the UE, application programs, and setting information. The storageunit 1520 may also store the information on a second access node forradio communication with a second radio access technology. The storageunit 1520 provides the stored information in response to a request fromthe controller 1530.

The controller 1530 controls overall operations of the UE. For example,the controller 1530 controls the baseband processor 1510 and the RFprocessor 1500 for transmitting and receiving signals. The controller1530 writes and reads data to and from the storage unit 1530. For thispurpose, the controller 1530 may include at least one processor. Forexample, the controller 1530 may include a communication processor (CP)for controlling communications and an application processor (AP) forcontrolling higher layer programs such as applications.

FIG. 16 is a block diagram illustrating a configuration of a basestation according to an embodiment of the present invention.

In reference to FIG. 16, the base station includes an RF processor 1600,a baseband processor 1610, a backhaul communication unit 1620, a storageunit 1630, and a controller 1640.

The RF processor 1600 has a function for transmitting/receiving a signalover a radio channel such as band conversion and amplification of thesignal. That is, the RF processing unit 1600 up-converts a basebandsignal from the baseband processor 1610 to an RF band signal andtransmits the RF signal via an antenna and down-converts the RF signalreceived via the antenna to a baseband signal. For example, the RFprocessor 1600 may include a transmission filter, a reception filter, anamplifier, a mixer, an oscillator, a DAC, and an ADC. Although oneantenna is depicted in FIG. 16, the base station may be provided with aplurality of antennas. The RF processor 1600 may also include aplurality of RF chains. The RF processor 1600 may perform beamforming.For beamforming, the RF processor 1600 may adjust the phase and size ofa signal to be transmitted/received by means of the antennas or antennaelements. The RF processor 1600 may be configured to transmit one ormore layers for a downlink MIMO operation.

The baseband processor 1610 has a baseband signal-bit string conversionfunction according to a physical layer standard of the system. Forexample, in a data transmission mode, the baseband processor 1610performs encoding and modulation on the transmission bit string togenerate complex symbols. In a data reception mode, the basebandprocessor 1610 performs demodulation and decoding on the baseband signalfrom the RF processor 1600 to recover the transmitted bit string. In thecase of using an OFDM scheme for data transmission, the basebandprocessor 1610 performs encoding and modulation on the transmission bitstring to generate complex symbols, maps the complex symbols tosubcarriers, performs inverse fast Fourier transform (IFFT) on thesymbols, and inserts a cyclic prefix (CP) into the symbols to generateOFDM symbols. In the data reception mode, the baseband processor 1610splits the baseband signal from the RF processor 1600 into OFDM symbols,performs fast Fourier transform (FFT) on the OFDM symbols to recover thesignals mapped to the subcarriers, and performs demodulation anddecoding on the signals to recover the transmitted bit string. Thebaseband processor 1610 and the RF processor 1600 process thetransmission and reception signals as described above. Accordingly, thebaseband processor 1610 and the RF processor 1600 may be referred to asa transmitter, a receiver, a transceiver, or a communication unit.

The backhaul communication unit 1620 provides an interface forcommunication with other nodes in the network. That is, the backhaulcommunication unit 1620 converts a bit string to be transmitted from thebase station to another node, e.g., another base station and corenetwork, to a physical signal and converts a physical signal receivedfrom another node to a bit string.

The storage unit 1630 stores data such as basic programs for operationof the base station, application programs, and setting information. Thestorage unit 1630 may also store the information on the bearersestablished for UEs and measurement results reported by the connectedUEs. The storage unit 1630 may also store the information for use by aUE in determining whether to enable or disable multi-connectivity. Thestorage unit 1630 may provide the stored data in reference to a requestfrom the controller 1640.

The controller 1640 controls overall operations of the base station. Forexample, the controller 1640 controls the baseband processor 1610, theRF processor 1600, and the backhaul communication unit 1620 fortransmitting and receiving signals. The controller 1640 writes and readsdata to and from the storage unit 1630. For this purpose, the controller1640 may include at least one processor.

A transmitter for transmitting a signal in a wireless communicationsystem includes a transmit unit configured to transmit the signal to areceiver and

a controller configured to control to check segment offset (SO)information and generate a first layer protocol data unit (PDU)including the SO information and control the transmit unit to transmitthe first layer PDU, wherein the first layer PDU includes at least oneheader and a second layer PDU group corresponding to the header and thesecond layer PDU group includes at least one second layer PDU. Areceiver for receiving a signal in a wireless communication systemincludes a receive unit configured to receive a signal from atransmitter and a controller configured to control the receive unit toreceive a first layer protocol data unit (PDU) including segment offset(SO) information, check the SO information, and recover a second layerPDU from the first layer PDU based on the SO information, wherein thefirst layer PDU includes at least one header and a second layer PDUgroup corresponding to the header and the second layer PDU groupincludes at least one second layer PDU. In the embodiments of thepresent inventions, the components are described in singular or pluralforms depending on the embodiment. However, the singular and pluralforms are selected appropriately for the proposed situation forexplanatory convenience only without any intention of limiting thepresent invention thereto; thus, the singular form includes the pluralforms as well, unless the context clearly indicates otherwise.

Although the description has been made with reference to particularembodiments, the present invention can be implemented with variousmodifications without departing from the scope of the present invention.Thus, the present invention is not limited to the particular embodimentsdisclosed, and it will include the following claims and theirequivalents.

1. A method performed by a transmitter in a communication system, themethod comprising: obtaining, by a medium access control (MAC) entity ofthe transmitter, a MAC service data unit (SDU); generating, by the MACentity, a MAC protocol data unit (PDU) including a MAC subheader and theMAC SDU; and sending, by the MAC entity, the MAC PDU to a lower layer,wherein the MAC subheader corresponds to the MAC SDU, wherein the MACsubheader to which the MAC SDU corresponds is placed immediately infront of the MAC SDU, and wherein the MAC subheader to which the MAC SDUcorresponds does not include an E field indicating whether another MACsubheader, MAC control element (CE), or MAC SDU follows.
 2. The methodof claim 1, wherein the MAC subheader to which the MAC SDU correspondsincludes a logical channel identifier (LCID) field.
 3. The method ofclaim 2, wherein the MAC subheader to which the MAC SDU correspondsfurther includes a length field.
 4. A method performed by a receiver ina communication system, the method comprising: receiving, by a mediumaccess control (MAC) entity of the receiver, a MAC protocol data unit(PDU) from a lower layer; identifying, by the MAC entity, a MAC servicedata unit (SDU) and a MAC subheader based on the MAC PDU; anddelivering, by the MAC entity, the MAC SDU, wherein the MAC subheadercorresponds to the MAC SDU, wherein the MAC subheader to which the MACSDU corresponds is placed immediately in front of the MAC SDU, andwherein the MAC subheader to which the MAC SDU corresponds does notinclude an E field indicating whether another MAC subheader, MAC controlelement (CE), or MAC SDU follows.
 5. The method of claim 4, wherein theMAC subheader to which the MAC SDU corresponds includes a logicalchannel identifier (LCID) field.
 6. The method of claim 5, wherein theMAC subheader to which the MAC SDU corresponds further includes a lengthfield.
 7. A transmitter in a communication system, the transmittercomprising: a transceiver; and a controller coupled with the transceiverand configured to: obtain, by a medium access control (MAC) entity ofthe transmitter, a MAC service data unit (SDU), generate, by the MACentity, a MAC protocol data unit (PDU) including a MAC subheader and theMAC SDU, and send, by the MAC entity, the MAC PDU to a lower layer,wherein the MAC subheader corresponds to the MAC SDU, wherein the MACsubheader to which the MAC SDU corresponds is placed immediately infront of the MAC SDU, and wherein the MAC subheader to which the MAC SDUcorresponds does not include an E field indicating whether another MACsubheader, MAC control element (CE), or MAC SDU follows.
 8. Thetransmitter of claim 7, wherein the MAC subheader to which the MAC SDUcorresponds includes a logical channel identifier (LCID) field.
 9. Thetransmitter of claim 8, wherein the MAC subheader to which the MAC SDUcorresponds further includes a length field.
 10. A receiver in acommunication system, the receiver comprising: a transceiver; and acontroller coupled with the transceiver and configured to: receive, by amedium access control (MAC) entity of the receiver, a MAC protocol dataunit (PDU) from a lower layer, identify, by the MAC entity, a MACservice data unit (SDU) and a MAC subheader based on the MAC PDU, anddeliver, by the MAC entity, the MAC SDU, wherein the MAC subheadercorresponds to the MAC SDU, wherein the MAC subheader to which the MACSDU corresponds is placed immediately in front of the MAC SDU, andwherein the MAC subheader to which the MAC SDU corresponds does notinclude an E field indicating whether another MAC subheader, MAC controlelement (CE), or MAC SDU follows.
 11. The receiver of claim 10, whereinthe MAC subheader to which the MAC SDU corresponds includes a logicalchannel identifier (LCID) field.
 12. The receiver of claim 11, whereinthe MAC subheader to which the MAC SDU corresponds further includes alength field.